Fluid bearing device

ABSTRACT

An object is to reduce manufacturing cost of a housing, and enable to disuse an adhesive in fixation portions between a housing and a bearing sleeve and the like. 
     A housing  7  is made of resin material, which comprises a liquid crystal polymer (LCP) as crystalline resin blended with carbon nanotubes in a blending ratio of 2 to 35 vol % as a conductive filler, by injection molding. A bearing sleeve  8 , which is inserted into the inner peripheral surface  7   c  of the housing  7 , is secured to the housing  7  by ultrasonic welding.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 10/557,257, filed Oct. 11, 2006, now pending; which was aNational Stage application of International Application No.PCT/JP2004/010177, filed Jul. 9, 2004, claiming the benefit of priorityof Japanese Patent Application No. 2003-278414, filed Jul. 23, 2003, Thedisclosures of the prior applications are hereby incorporated byreference herein in their entirety.

TECHNICAL FIELD

The present invention relates to a fluid bearing device which supportsan axial member in a non-contact manner by an oil film of a lubricatingoil generated in a radial bearing gap. This bearing device is ideal foruse in information equipment, including the spindle motors for magneticdisk devices such as HDD and FDD, optical disk devices for CD-ROM,CD-R/RW, DVD-ROM/RAM, etc. and magneto-optical disk devices for MD, MO,etc., the polygon scanner motors in laser beam printers (LBP), orsmall-scale motors for electrical equipment such as axial flow fans.

BACKGROUND ART

Speedup, cost reduction, noise reduction, and the like are required ofthe foregoing various motors, in addition to high accuracy in rotation.One of components to determine required performance is a bearing forsupporting a spindle of the motor. In recent years, a fluid bearinghaving superior characteristics in the foregoing required performance iscontemplated using, or actually used.

This type of fluid bearing is broadly divided into a dynamic pressurebearing and a so-called cylindrical bearing (a bearing the bearingsurface of which is in the shape of a perfect circle). The dynamicpressure bearing is provided with dynamic pressure generation meanswhich makes a lubricating oil in a bearing gap generate dynamicpressure. The cylindrical bearing is not provided with such dynamicpressure generation means.

Taking the case of a fluid bearing device which is installed in thespindle motor of the disk device such as the HDD and the like, forexample, the fluid bearing device is provided with a radial bearingportion for supporting an axial member in a non-contact manner rotatablyin a radial direction, and a thrust bearing portion for supporting theaxial member rotatably in a thrust direction. As the radial bearingportion, a dynamic bearing, which is provided with grooves (dynamicpressure generating grooves) in the inner peripheral surface of abearing sleeve or in the outer peripheral surface of the axial member togenerate dynamic pressure, is used. As the thrust bearing portion, forexample, a dynamic bearing, which is provided with dynamic pressuregenerating grooves in both end faces of a flange part of the axialmember, or in surfaces opposed thereto (an end face of a bearing sleeve,an end face of a thrust member fixed on a housing or the like), is used(refer to, for example, Japanese Patent Laid-Open Publication No.2000-291648). Otherwise, there are cases where a bearing (so-calledpivot bearing), which supports one end face of the axial member in acontact manner by a thrust plate, is used as the thrust bearing portion(refer to, for example, Japanese Patent Laid-Open Publication No.11-191943).

The bearing sleeve is generally fixed in a predetermined position of theinner periphery of the housing. A seal member is disposed on an openingof the housing in most cases, in order to prevent the lubricating oil inan internal space of the housing from leaking to the outside.

The fluid bearing device having a construction described above comprisesparts such as a housing, a bearing sleeve, an axial member, a thrustmember, and a seal member, and an effort is under way to increase theaccuracy of finishing and assembling of each part, for the purpose ofensuring high bearing performance, which is required in accordance withincrease in the performance of the information equipment more than ever.Demand for cost reduction on this type of fluid bearing device, on theother hand, has increasingly become stringent in accords with a tendencytoward drop in price of the information equipment.

One of important points for reducing cost of this type of fluid bearingdevice is efficiency in an assembling process. Namely, the housing andthe bearing sleeve, the housing and the thrust member, and the housingand the seal member are generally bonded to each other by use of anadhesive in most cases. However, it takes relatively long time fromapplication of the adhesive to solidification thereof, so that bondingis part of the reason of reducing the efficiency in the assemblingprocess. Also, there is concern about the occurrence of outgassing dueto the adhesive, as well as the possibility of degradation of adhesionwith a lapse of time.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a fluid bearing deviceat further lower cost by reducing manufacturing cost of a housing inthis type of fluid bearing device, and by enabling to disuse an adhesivein a fixation portion between a housing and a bearing sleeve and thelike to increase efficiency in an assembling process.

Another object of the present invention is to provide a fluid bearingdevice which can restrain the occurrence of outgassing from a fixationportion between parts and degradation of adhesion with a lapse of time.

To achieve the objects described above, the present invention provides afluid bearing device comprising a housing, a bearing sleeve disposedinside the housing, an axial member inserted into an inner peripheralsurface of the bearing sleeve, and a radial bearing portion forsupporting the axial member in a non-contact manner in a radialdirection by an oil film of a lubricating oil formed in a radial bearinggap between the inner peripheral surface of the bearing sleeve and anouter peripheral surface of the axial member. In this fluid bearingdevice, the housing is made of one type of resin material selected fromamong amorphous resin blended with a filler in a blending ratio of 3 to35 vol %, and crystalline resin blended with a filler in a blendingration of 2 to 30 vol %, and the bearing sleeve is fixed to the housingby welding.

The housing made of resin can be formed by molding such as injectionmolding and the like. Thus, it is possible to manufacture the resinhousing at lower cost as compared with a metal housing, which is formedby machining such as turning and the like. Also the resin housing cansecure relatively high accuracy as compared with the metal housingformed by press working.

By fixing the bearing sleeve on the housing by use of welding, it ispossible to increase working efficiency as compared with conventionalfixation using an adhesive. Also it is possible to prevent or restrainthe occurrence of outgassing from a fixation portion and degradation ofadhesion with a lapse of time.

Herein, “welding” refers to a phenomenon in which a joint surface of oneor both of two members to be joined is melted and then solidified to befixed. It is possible to appropriately select and adopt means forwelding from among, for example, ultrasonic welding, vibration welding,high frequency induction heating welding, hot plate welding, and thelike in accordance with material of the member to be joined, a jointcondition, and other various conditions. Generally, the ultrasonicwelding is a method for generating high frictional heat in a part of aresin product by applying ultrasonic vibration and welding pressure atthe same time, in order to melt and fix a joint surface. The vibrationwelding is a method for melting and fixing the joint surfaces byvibrating the two members to be joined in a predetermined direction withapplying pressure. The high frequency induction heating welding is amethod by which the member to be joined is subjected to a high-frequencymagnetic field. Heat is generated by overcurrent loss, and hence thejoint surface is melted and fixed. The hot plate welding is a method bywhich a heat source (a hot plate) at high temperature is brought intocontact with the joint surface of a resin product, in order to melt andfix the joint surface. Of these welding methods, the ultrasonic weldingis especially preferable, because the ultrasonic welding needs justsimple equipment and its welding operation can be carried out in a shorttime.

When the housing is made of amorphous resin, it is necessary to considerthe following matters. Namely, the amorphous resin is generally superiorin the ability of welding, when it is welded by the ultrasonic weldingand the like. Thus, when the bearing sleeve is fixed on the housing madeof amorphous resin by welding, it is possible to provide a firm andstable fixation state between them. The amorphous resin, on the otherhand, tends to be inferior in oil resistance to the crystalline resin.If stress such as residual stress due to welding and the like is appliedand the amorphous resin housing is in contact with the lubricating oilcharged into an internal space, there is a possibility that a stresscrack occurs in the housing. This stress crack is a phenomenon, in whicha crack (sometimes called “solvent crack”) occurs, when the resin makescontact with the lubricating oil (solvent) under predetermined stress,and the lubricating oil penetrates and diffuses into the resin. Thecrack due to contact with the lubricating oil hardly occurs under nostress, but such a phenomenon may occur under the predetermined stress.

Thus, to prevent the degradation of the housing due to the stress crack,a blending ratio of the filler into the amorphous resin is regulated ina range equal to or less than 35 vol %. The amorphous resin is generallysuperior in the ability of welding, as described above, but the abilityof welding tends to decrease with increase in blending quantity of thefiller. Thus, if the blending quantity is too much, it becomes necessaryto enhance a welding condition such as welding time and the like, inorder to secure required fixation strength of the fixation portion(welded portion). Since the residual stress in welding increases inaccordance therewith, resistance to the stress cracking of the housingbecomes insufficient. Regulating the blending ratio of the filler intothe amorphous resin equal to or less than 35 vol % makes it possible toprevent inconvenience like this, and secure favorable resistance tocracking of the housing. If the blending quantity of the filler is toolittle, on the other hand, an original purpose of blending the filler,in other words, a purpose of providing characteristics such as requiredstrength, dimensional stability against variation in temperature,conductivity, and the like to the housing is lost. Therefore, theblending ratio of the filler into the amorphous resin is regulated in arange equal to or more than 3 vol %, in order to secure the requiredcharacteristics of the housing.

The crystalline resin is superior in the oil resistance, but inferior inthe ability of welding to the amorphous resin. Thus, in a case that thehousing is made of the crystalline resin, if the blending quantity ofthe filler is too much, required fixation strength of the fixationportion (welded portion) cannot be secured due to decrease in theability of welding. Therefore, the blending ratio of the filler into thecrystalline resin is regulated in a range equal to or less than 30 vol%, in order to secure the necessary ability of welding and the requiredfixation strength of the fixation portion (welded portion). If theblending quantity of the filler is too little, on the other hand, anoriginal purpose of blending the filler, in other words, a purpose ofproviding characteristics such as required strength, dimensionalstability against variation in temperature, conductivity and the like tothe housing is lost. Therefore, the blending ratio of the filler intothe crystalline resin is regulated in a range equal to or more than 2vol %, in order to secure the required characteristics of the housing.

The present invention further provides a fluid bearing device comprisinga housing, a bearing sleeve disposed inside the housing, an axial memberinserted into an inner peripheral surface of the bearing sleeve, aradial bearing portion for supporting the axial member in a non-contactmanner in a radial direction by an oil film of a lubricating oil formedin a radial bearing gap between the inner peripheral surface of thebearing sleeve and an outer peripheral surface of the axial member, anda thrust bearing portion for supporting the axial member in a thrustdirection. In this fluid bearing device, the housing may be made of theforegoing resin material, and at least one of the bearing sleeve and athrust member composing the thrust bearing portion may be fixed on thehousing by welding. When only one of the bearing sleeve and the thrustmember is fixed by welding, a method such as insert molding, pressfitting and the like may be adopted as a method for fixing the other oneon the housing. By, for example, molding (injection molding and thelike) the housing out of the foregoing resin material with the use of aninsert part of the bearing sleeve, it is possible to fix the bearingsleeve on the housing without additional fixing operation.

Further the present invention provides a fluid bearing device comprisinga housing, a bearing sleeve disposed inside the housing, an axial memberinserted into an inner peripheral surface of the bearing sleeve, aradial bearing portion for supporting the axial member in a non-contactmanner in a radial direction by an oil film of a lubricating oil formedin a radial bearing gap between the inner peripheral surface of thebearing sleeve and an outer peripheral surface of the axial member, anda seal portion for sealing the inside of the housing. In this fluidbearing device, the housing may be made of the foregoing resin material,and at least one of the bearing sleeve and a seal member composing theseal portion is fixed on the housing by welding. When only one of thebearing sleeve and the seal member is fixed by welding, a method such asinsert molding, press fitting, and the like may be adopted as a methodfor fixing the other one on the housing.

Further the present invention provides a fluid bearing device comprisinga housing, a bearing sleeve disposed inside the housing, an axial memberinserted into an inner peripheral surface of the bearing sleeve, aradial bearing portion for supporting the axial member in a non-contactmanner in a radial direction by an oil film of a lubricating oil formedin a radial bearing gap between the inner peripheral surface of thebearing sleeve and an outer peripheral surface of the axial member, athrust bearing portion for supporting the axial member in a thrustdirection, and a bottom member for closing the bottom of the housing. Inthis fluid bearing device, the housing may be made of the foregoingresin material, and at least one of the bearing sleeve and the bottommember is fixed on the housing by welding. When only one of the bearingsleeve and the bottom member is fixed by welding, a method such asinsert molding, press fitting, and the like may be adopted as a methodfor fixing the other one on the housing.

The resin for forming the housing is not limited to particular one aslong as it is a thermoplastic resin. In the case of the amorphous resin,for example, polysulfone (PSF), polyethersulfone (PES),polyphenylsulfone (PPSF), or polyetherimide (PEI) is available. In thecase of the crystalline resin, for example, liquid crystal polymer(LCP), polyether ether ketone (PEEK), polybutylene terephthalate (PBT),or polyphenylene sulfide (PPS) is available.

A kind of the filler charged into the resin is not especially limited,but, for example, a fibrous filler such as glass fiber and the like, awhisker filler such as potassium titanate and the like, a scalelikefiller such as mica and the like, or a fibrous or powdery conductivefiller such as carbon fiber, carbon black, graphite, carbonnanomaterial, metal powder, and the like is available as the filler.

In a fluid bearing device installed in a spindle motor for a disk drivedevice such as a HDD and the like, for example, electrical conductivitymay be required of a housing, in order to let static electricity, whichis caused by friction between a disk such as an magnetic disk and thelike and air, escape to a ground. In such a case, blending the foregoingconductive filler into resin forming the housing makes it possible toprovide the housing with the electrical conductivity.

The carbon nanomaterial is preferable as the foregoing conductivefiller, in terms of high electrical conductivity, high dispersibility ina resin matrix, high resistance to abrasive wear, low outgassing, andthe like. Carbon nanofiber is preferable as the carbon nanomaterial. Thecarbon nanofiber includes material called “carbon nanotube,” which has adiameter of from 40 nm to 50 nm.

Single-layer carbon nanotube, multilayer carbon nanotube,cup-stacked-type carbon nanofiber, vapor-phase grown carbon fiber, andthe like are known as concrete examples of the carbon nanofiber, and anyof them is available in the present invention. The carbon nanofiber maybe used singly or by blending two or more types thereof. Furthermore,the carbon nanofiber may be blended with another filler.

According to the present invention, as described above, it is possibleto reduce manufacturing cost of the housing. Furthermore, the fluidbearing device enables to disuse an adhesive in the fixation portionbetween the housing and the bearing sleeve and the like, so that it ispossible to increase efficiency in an assembling process. Therefore, itis possible to provide the fluid bearing device at further lower cost.

According to the present invention, it is possible to restrain theoccurrence of outgassing from the fixation portion between parts, anddegradation of adhesion with a lapse of time. Therefore, it is possibleto provide the fluid bearing device which is superior in quality anddurability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a spindle motor for information equipmentwhich uses a fluid bearing device according to the present invention;

FIG. 2 is a sectional view of a fluid bearing device according to anembodiment of the present invention;

FIG. 3 is a sectional view of a fluid bearing device according toanother embodiment of the present invention; and

FIG. 4 is a sectional view of a fluid bearing device according tofurther another embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described hereinafter.

FIG. 1 schematically shows an example of the structure of a spindlemotor for information equipment, in which a fluid bearing device (fluiddynamic bearing device) 1 according to this embodiment is installed.This spindle motor is used in a disk drive device such as a HDD and thelike. The spindle motor is provided with the fluid bearing device 1 forratatably supporting an axial member 2 in a non-contact manner, a rotor(disk hub) 3 attached to the axial member 2, and a stator 4 and a rotormagnet 5 which are opposed to each other with a gap in a radialdirection. The stator 4 is attached to the outer periphery of a bracket6, and the rotor magnet 5 is attached to the inner periphery of the diskhub 3. A housing 7 of the fluid bearing device 1 is attached into theinner periphery of the bracket 6. The disk hub 3 holds one or aplurality of disks D such as a magnetic disk and the like. When thestator 4 is energized, the rotor magnet 5 is rotated by electromagneticforce generated between the stator 4 and the rotor magnet 5, and hencethe disk hub 3 and the axial member 2 are integrally rotated.

FIG. 2 shows the fluid bearing device 1. The fluid bearing device 1comprises the housing 7, a bearing sleeve 8 and a thrust member 10 whichare fixed on the housing 7, and the axial member 2. A first radialbearing portion R1 and a second radial bearing portion R2 are providedseparately in an axial direction between the inner peripheral surface 8a of the bearing sleeve 8 and the outer peripheral surface 2 a 1 of anaxial part 2 a of the axial member 2. Also, a first thrust bearingportion T1 is provided between the lower end face 8 c of the bearingsleeve 8 and the upper end face 2 b 1 of a flange part 2 b of the axialmember 2. A second thrust bearing portion T2 is provided between the endface 10 a of the thrust member 10 and the lower end face 2 b 2 of theflange part 2 b. For the convenience of explanation, the side of thethrust member 10 is referred to as a lower side, and the opposite sideof the thrust member 10 is referred to as an upper side in explanationbelow.

The housing 7 is made of resin material, which comprises a liquidcrystal polymer (LCP) as crystalline resin blended with carbon nanotubesin a blending ration of 2 to 30 vol % as a conductive filler, byinjection molding. The housing 7 is provided with a cylindrical sideportion 7 b, and a ring-shaped seal portion 7 a which integrally extendsfrom the upper end of the side portion 7 b on the side of an internaldiameter. The inner peripheral surface 7 a 1 of the seal portion 7 a isopposed to a tapered surface 2 a 2 provided on the outer periphery ofthe axial part 2 a across predetermined seal space S. A diameter of thetapered surface 2 a 2 of the axial part 2 a gradually decreases in anupward direction (outward with respect to the housing 7), and thetapered surface 2 a 2 functions as a centrifugal force seal by therotation of the axial member 2.

The axial member 2 is made of, for example, metal material such asstainless steel and the like. The axial member 2 is provided with theaxial part 2 a and the flange part 2 b, which is integrally orseparately provided on the lower end of the axial part 2 a.

The bearing sleeve 8 is made of, for example, porous material comprisingsintered metal, and more particularly, porous material of sintered metalthe principal ingredient of which is copper, in the shape of a cylinder.The bearing sleeve 8 is fixed in a predetermined position on the innerperipheral surface 7 c of the housing 7.

Upper and lower two regions, being radial bearing surfaces of the firstradial bearing portion R1 and the second radial bearing portion R2, areprovided in the inner peripheral surface 8 a of the bearing sleeve 8made of sintered metal separately in the axial direction. In each of thetwo regions, dynamic pressure generating grooves 13 in the shape of, forexample, a herringbone are formed.

Dynamic pressure generating grooves in the shape of, for example, aspiral or a herringbone are formed in the lower end face 8 c of thebearing sleeve 8, which functions as a thrust bearing surface of thefirst thrust bearing portion T1.

The thrust member 10, which is made of, for example, resin material ormetal material such as brass and the like, is fixed to the lower end ofthe inner peripheral surface 7 c of the housing 7. Dynamic pressuregenerating grooves in the shape of, for example, a herringbone or aspiral are formed in an end face 10 a of the thrust member 10, whichfunctions as a thrust bearing surface of the second thrust bearingportion T2.

The fluid bearing device 1 according to this embodiment is assembled by,for example, the following procedure.

First, the bearing sleeve 8 is inserted into the inner peripheralsurface 7 c of the housing 7, in such a manner that the upper end face 8b thereof makes contact with the inner surface 7 a 2 of the seal portion7 a. Thus, the axial position of the bearing sleeve 8 with respect tothe housing 7 is determined. In this state, the bearing sleeve 8 isfixed on the housing 7 by ultrasonic welding. Since the crystallineresin in which a blending ratio of the filler is regulated in a range of2 to 30 vol % is used as the resin material for forming the housing 7,as described above, it has the high ability of welding during theultrasonic welding. Thus, it is possible to obtain a favorable andstable fixation state of the bearing sleeve 8. Furthermore, since thebearing sleeve 8 is made of the sintered metal of the porous material,melting resin in a joint surface of the housing 7 enters internal poresof the bearing sleeve 8 from surface openings (an area in which theinternal pores of porous texture of the sintered metal are open to asurface) in a joint surface of the bearing sleeve 8, and solidifies.Because portions which have solidified in the internal pores bring thehousing 7 into tightly contact with the bearing sleeve 8 by use of akind of anchor effect, both of the housing 7 and the bearing sleeve 8 donot relatively deviate, so that it is possible to obtain a firm andstable fixation state. Since the crystalline resin has high oilresistance, degradation by a stress crack is hard to occur in thehousing 7, and hence the housing 7 has favorable durability.Furthermore, since the carbon nanotubes are blended as the conductivefiller, the housing 7 has electrical conductivity though it is made ofresin.

Then, the axial member 2 is attached to the bearing sleeve 8. Afterthat, the thrust member 10 is attached into the lower end of the innerperiphery 7 c of the housing 7 and fixed in a predetermined position.Then, they are fixed by ultrasonic welding. Since the housing 7 is madeof the foregoing resin material, it has the high ability of weldingduring the ultrasonic welding. Thus, it is possible to obtain afavorable and stable fixation state of the thrust member 10. Providingprojections and depressions in the shape of knurls, screws and the likeon the outer peripheral surface of the thrust member 10 can effectivelyincrease fixation force by welding.

When assembly is completed as described above, the axial part 2 a of theaxial member 2 is inserted into the inner peripheral surface 8 a of thebearing sleeve 8, and the flange part 2 b is contained in a spacebetween the lower end face 8 c of the bearing sleeve 8 and the end face10 a of the thrust member 10. Then, an internal space of the housing 7tightly sealed by the seal portion 7 a, including the internal pores ofthe bearing sleeve 8, is filled with a lubricating oil. The oil level ofthe lubricating oil is maintained within the confines of a seal space S.

When the axial member 2 rotates, each of the regions (the upper andlower two regions) being the radial bearing surfaces in the innerperipheral surface 8 a of the bearing sleeve 8 is opposed to the outerperipheral surface 2 a 1 of the axial part 2 a across a radial bearinggap. The region being the thrust bearing surface in the lower end face 8c of the bearing sleeve 8 is opposed to the upper end face 2 b 1 of theflange section 2 b across a thrust bearing gap. The region being thethrust bearing surface in the end face 10 a of the thrust member 10 isopposed to the lower end face 2 b 2 of the flange part 2 b across athrust bearing gap. Dynamic pressure of the lubricating oil is generatedin the foregoing radial bearing gaps in accordance with the rotation ofthe axial member 2, and hence oil films of the lubricating oil formed inthe foregoing radial bearing gaps support the axial part 2 a of theaxial member 2 in a non-contact manner rotatably in the radialdirection. Thus, the first radial bearing portion R1 and the secondradial bearing portion R2 for supporting the axial member 2 in anon-contact manner rotatably in the radial direction are configured. Atthe same time, dynamic pressure of the lubricating oil is generated inthe foregoing thrust bearing gaps, and hence oil films of thelubricating oil formed in the foregoing thrust bearing gaps support theflange part 2 b of the axial member 2 in a non-contact manner rotatablyin both thrust directions. Thus, the first thrust bearing portion T1 andthe second thrust bearing portion T2 for supporting the axial member 2in a non-contact manner rotatably in the thrust direction areconfigured.

In the foregoing structure, only one of the bearing sleeve 8 and thethrust member 10 may be fixed on the housing 7 by welding, and the othermay be fixed by means except for welding such as, for example, insertmolding, press fitting, and the like. The housing 7 may be made ofamorphous resin blended with a filler in a blending ratio of 3 to 35 vol%.

FIG. 3 shows a fluid bearing device 11 according to another embodiment.The substantial differences between the fluid bearing device 11according to this embodiment and the fluid bearing device 1 shown inFIG. 2 are that the seal portion is composed of a separate seal member12, and the seal member 12 is fixed on the upper end of the innerperipheral surface 7 c of the housing 7 by welding. The seal member 12made of, for example, metal material or resin material is welded to ajoint surface of the housing 7 by ultrasonic welding. The innerperipheral surface 12 a of the seal member 12 is opposed to the taperedsurface 2 a 2 provided on the outer periphery of the axial part 2 aacross a predetermined seal space S. The seal member 12 may be fixed onthe housing 7 by means except for welding such as, for example, insertmolding (in a case that the seal member 12 is made of metal material),press fitting, and the like. The other matters are the same as theforegoing embodiment, and hence duplicate explanation is omitted.

In a case that the seal portion is composed of the separate seal member,if the housing is made of the foregoing resin material in the shape of acylinder with a bottom, and a thrust bearing surface for structuring thesecond thrust bearing portion T2 is provided in the inner bottom face ofthe bottom of the housing, it is possible to omit the thrust member. Inthis case, the dynamic pressure generating grooves formed in the thrustbearing surface can be molded at the same time as the molding of thehousing (a molding portion for molding the dynamic pressure generatinggrooves is formed in a mold for molding the housing).

FIG. 4 shows a fluid bearing device 21 according to further anotherembodiment. The substantial difference between the fluid bearing device21 according to this embodiment and the fluid bearing device 1 shown inFIG. 2 is that a bottom member 11 for closing an opening of the bottomof the housing 7 is fixed on the bottom end of the inner peripheralsurface 7 c of the housing 7 by welding after a thrust member 10′ isattached to the bottom end.

In this embodiment, the thrust member 10′ is integrally provided with aring-shaped contact portion 10 b′, which extends upward from the outerperipheral edge of an end face 10 a′ of the thrust member 10′. The upperend face of the contact portion 10 b′ makes contact with the lower endface 8 c of the bearing sleeve 8, and the inner peripheral surface ofthe contact portion 10 b′ is opposed to the outer peripheral surface ofthe flange part 2 b across a gap.

The bottom member 11 is made of, for example, resin material. The topface of the bottom member 11 makes contact with the bottom face of thethrust member 10′.

After the bearing sleeve 8 and the axial member 2 are assembled in themanner described above, the thrust member 10′ is inserted into the lowerend of the inner peripheral surface 7 c of the housing 7 and the upperend face of the contact section 10 b′ makes contact with the lower endface 8 c of the bearing sleeve 8. Thus, the axial position of the thrustmember 10′ with respect to the bearing sleeve 8 is determined. Bycontrolling axial dimensions of the contact portion 10 b′ and the flangepart 2 b, it is possible to set the thrust bearing gaps of the firstthrust bearing portion T1 and the second thrust bearing portion T2 withhigh accuracy. Then, the bottom member 11 is attached to the lower endof the inner peripheral surface 7 c, in such a manner that the top faceof the bottom member 11 makes contact with the bottom face of the thrustmember 10′. In this state, the bottom member 11 is fixed on the housing7 by ultrasonic welding. The other matters are the same as the foregoingembodiment, and hence duplicate explanation is omitted.

The present invention can be applied in a like manner to a fluid bearingdevice which adopts a so-called pivot bearing as the thrust bearingportion, or a fluid bearing device which adopts a so-called cylindricalbearing as a radial bearing portion.

As to dynamic bearing devices having the structure shown in FIG. 4, theability of welding in a welded portion between the housing 7 and thebottom member 11 (hereinafter simply called “welded portion”) isevaluated, with the use of dynamic bearing devices in which the housing7 and the bottom member 11 made of LCP being crystalline resin are fixedto each other by ultrasonic welding (Examples 1 to 4, ComparativeExample 1), and dynamic bearing devices in which the housing 7 and thebottom member 11 made of PES being amorphous resin are fixed to eachother by ultrasonic welding (Examples 5 to 7, Comparative Examples 2 and3). In each of the Examples and Comparative Examples, a filler isblended into resin forming the housing 7 and the bottom member 11 in ablending ratio shown in tables 1 and 2, so that each volumeresistibility becomes 10⁶Ω·cm.

The ability of welding is rated on a scale of ◯ (good), Δ (slightlyinferior), and x (inferior) in regard to the following evaluation items.Tables 1 and 2 show the results of the evaluation.

TABLE 1 Crystalline resin (LCP) Comparative Example 1 Example 2 Example3 Example 4 Example 1 Blending 29 25 23 15 34 ratio of filler (vol %)Strength 51 71 80 93 31 of welded portion (%) Sealability ◯ ◯ ◯ ◯ ΔLeakage ◯ ◯ ◯ ◯ Δ of oil Thermal ◯ ◯ ◯ ◯ — shock

TABLE 2 Amorphous resin (PES) Exam- Exam- Exam- Comparative Comparativeple 5 ple 6 ple 7 Example 2 Example 3 Blending ratio 33 28 20 38 43 offiller (vol %) Strength of 51 71 80 43 35 welded portion (%) Sealability◯ ◯ ◯ ◯ Δ Leakage of oil ◯ ◯ ◯ X X Thermal shock ◯ ◯ ◯ — —

[Strength of Welded Portion]

The strength of the welded portion in complete welding is calculatedfrom material properties of the resin, which forms the housing 7 and thebottom member 11, and a tab for welding (calculated value). Also, thestrength of the welded portion is actually measured (measured value).The measured value is divided by the calculated value to obtain astrength percentage of the welded portion, and the strength of thewelded portion is evaluated by use of the strength percentage.

[Sealability]

The sealability of the welded portion is evaluated by an He leak tester.

[Leakage of Oil]

The leakage of oil from the welded portion is mainly caused by a stresscrack due to residual stress applied to the welded portion. After thebottom member 11 is welded to the housing 7, the internal space of thehousing 7 is filled with diester oil. After holding the dynamic bearingdevice for six hours at an ambient temperature of 70 degrees Celsius,the presence or absence of the leakage of oil from the welded portionand the degree thereof are visually confirmed.

[Thermal Shock]

Resistance to thermal shock of the welded portion is evaluated. As inthe case of an oil-leakage test, after the bottom member 11 is welded tothe housing 7, the internal space of the housing 7 is filled withdiester oil. Then, the dynamic bearing device is held for one hour at anambient temperature of −40 degrees Celsius, and is held for another onehour at an ambient temperature of 100 degrees Celsius. This cycle isrepeated for 20 times, and then thermal shock is applied. After that,the leakage of oil from the welded portion is visually confirmed.

According to the foregoing evaluation tests, the Examples 1 to 7obtained good results with respect to each of the evaluation items ofthe strength of the welded portion, the sealability, the leakage of oil,and the thermal shock. The Comparative Examples 1 and 3 could not obtainsatisfied results with respect to each of the evaluation items of thestrength of the welded portion, the sealability, and the leakage of oil.The Comparative Example 2 obtained a good result with respect to thesealability, but could not obtain satisfied results with respect to eachof the evaluation items of the strength of the welded portion, and theleakage of oil. As for the Comparative Examples 1 to 3, a thermal shocktest was not carried out because they did not show satisfied results inthe oil-leakage test.

1. A fluid bearing device comprising: a housing, a bearing sleevedisposed inside the housing, an axial member inserted into an innerperipheral surface of the bearing sleeve, and a radial bearing portionfor supporting the axial member in a non-contact manner in a radialdirection by an oil film of a lubricating oil formed in a radial bearinggap between the inner peripheral surface of the bearing sleeve and anouter peripheral surface of the axial member, wherein the bearing sleeveis made of a sintered metal, an internal space of the housing, whichincludes an internal air hole defined in the bearing sleeve, is filledwith the lubricating oil, the housing is made of an amorphous resinblended with a filler in a blending ratio of 3 to 35 vol %, and thebearing sleeve is fixed to the housing by welding.
 2. The fluid bearingdevice according to claim 1, further comprising a thrust bearing portionfor supporting the axial member in a thrust direction, wherein a thrustmember of the thrust bearing portion is fixed to the housing by welding.3. The fluid bearing device according to claim 1, further comprising aseal portion for sealing the inside of the housing, wherein a sealmember of the seal portion is fixed to the housing by welding.
 4. Thefluid bearing device according to claim 1, wherein the amorphous resinis one resin selected from the group consisting of polysulfone (PSF),polyethersulfone (PES), polyphenylsulfone (PPSF), and polyetherimide(PEI).
 5. The fluid bearing device according to claim 1, wherein thefiller is conductive material.
 6. The fluid bearing device according toclaim 2, wherein the filler is conductive material.
 7. The fluid bearingdevice according to claim 3, wherein the filler is conductive material.8. The fluid bearing device according to claim 5, wherein the conductivematerial is carbon nanomaterial.
 9. The fluid bearing device accordingto claim 6, wherein the conductive material is carbon nanomaterial. 10.The fluid bearing device according to claim 7, wherein the conductivematerial is carbon nanomaterial.
 11. The fluid bearing device accordingto claim 1, further comprising a bottom member for closing a bottom ofthe housing, wherein the bottom member is fixed to the housing bywelding.